Closing unit for an injection molding machine

ABSTRACT

A closing unit for an injection molding machine includes a substantially C-shaped machine frame, to the first leg of which is mounted a stationary mold mounting plate and to the second leg of which is mounted a closing mechanism for driving a moveable mold mounting plate. The free ends of the legs of the machine frame are deformed under the influence of the closing force occurring during the closing operation. The stationary mold mounting plate is supported at or near its lower edge by a support element on the machine frame against the closing force and is fixedly connected above the lower edge to the first leg. The support element has a flexural beam extending transversely relative to the longitudinal axis of the machine, and a compression bar extending in the direction of the longitudinal axis of the machine.

BACKGROUND OF THE INVENTION

The invention concerns a closing unit for an injection molding machine, and a tie-bar-less injection molding machine having such a closing unit.

A closing unit of the general kind set forth is disclosed for example in DE 101 21 306 A1. The change in the orientation of the stationary mold mounting plate, that is caused per se by the closing force, is compensated in part by the support element and in part by the geometrical configuration of the free leg of the machine frame, to which the stationary mold mounting plate is connected. That design permits the stationary mold mounting plate to be fixedly mounted to the free leg of the machine frame and thus avoids the disadvantages of a pivotal mounting of the stationary mold mounting plate. The geometrical configuration required for that purpose for the free leg can be ascertained for example by calculation or experiments.

In the closing unit shown there, the support element comprises a compression bar which is in the form of an extension on the stationary mold mounting plate and which extends in the direction of the longitudinal axis of the machine and which under the closing force presses loosely against a flexural beam extending transversely relative to the longitudinal axis of the machine. High line loadings occur between the compression bar and the flexural beam. The strong internal frictional effects of the support element, that are linked thereto, adversely affect the functionality of the closing unit due to tribocorrosion (fretting corrosion) and shorten the service life of the support element.

In addition it has proven to be difficult to find satisfactory matching of upsetting by way of the compression bar and flexing by way of the flexural beam with that construction.

SUMMARY OF THE INVENTION

The object of the invention is to provide a closing unit for an injection molding machine and a tie-bar-less injection molding machine having such a closing unit, in which at least the problem of strong internal frictional effects does not arise.

That object is attained by a closing unit having the features of claim 1 and a tie-bar-less injection molding machine have such a closing unit.

The problem of tribocorrosion can be avoided by the backlash-free connection of the flexural beam to the machine frame (for example by screwing). Preferred embodiments of the invention are defined in the dependent claims.

There can be provided a further flexural beam which extends transversely relative to the longitudinal axis of the machine and which is fixedly connected to the stationary mold mounting plate.

The use of two flexural beams which are fixedly connected together by the compression bar makes it possible to ideally select upsetting and flexing in the support element easily by way of experiments.

On the basis of the flexing of each individual flexural beam and the upsetting of the compression bar it is possible to ascertain approximately (by hand) an overall stiffness which upon transmission of the closing force (for example about ⅓ of the total closing force) causes the required flexing effect (here about 0.5 mm). The required flexing arises out of the requirement that the stationary mold mounting plate is to remain vertical under load. This means that the difference between the deformation of the machine frame at the support of the stationary mold mounting plate in its upper region and the deformation of the machine frame in the region of the lower edge must be absorbed by the support element. More precise ascertainment can be effected by way of a calculation by means of finite elements. Fine tuning can be effected directly at the injection molding machine. It is possible there to measure the positions of the stationary mold mounting plate (top/bottom/left/right), at which closing forces are transmitted, and what the closing forces are.

Because the compression bar is fixedly connected (directly or indirectly) to both flexural beams, no internal frictional effects occur.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and details of the invention will be apparent from the Figures and the specific description relating thereto, in which:

FIG. 1 shows an injection molding machine according to the present invention;

FIG. 2 is a plan view of the injection molding machine of FIG. 1;

FIG. 3 shows a modified version of the injection molding machine of FIG. 1;

FIG. 4 is a detail view of the modified injection molding machine of FIG. 3;

FIG. 5 shows a further modified version of the injection molding machine of FIG. 1;

FIG. 6 shows the further modified version of the injection molding machine of FIG. 5 with detached support elements; and

FIG. 7 shows a closing unit of the injection molding machine of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an injection molding machine in a viewing direction inclinedly from above on to the machine frame 1. A stationary and a moveable mold mounting plate 3, 5 are arranged on the machine frame 1 in known manner. It is also possible to see a closing mechanism for moving the moveable mold mounting plate 5 relative to the stationary mold mounting plate 3 in the direction of the longitudinal axis L of the machine. The stationary mold mounting plate 3 has a nozzle opening 10, into which a nozzle of an injection assembly (not shown) can be introduced. It is further possible to see a support element 7 which in this embodiment comprises a further flexural beam 73 fixedly connected to the stationary mold mounting plate 3 by screwing, a compression bar 72 connected to the flexural beam 73, and a flexural beam 71. The flexural beam 71 is connected to the one leg 2. According to the invention the flexural beam 71 is connected free from backlash to the machine frame 1.

In the present case the two legs 2, 4 are respectively formed from two side plates of the machine frame 1, the side plates being arranged in mutually spaced relationship transversely relative to the longitudinal axis of the injection molding machine.

The fixing of the stationary mold mounting plate 3 above its lower edge 6 to the machine frame 1 is selected so as to that approximately two thirds of the closing force are being transmitted into the machine frame 1. The remaining third is diverted into the machine frame 1 by way of the support element 7. That portion can be varied by a change in the height of the fixed arrangement of the stationary mold mounting plate 3 above the lower edge 6. The support element 7 can remain in the lower region of the stationary mold mounting plate 3 and does not adversely affect the arrangement of the injection unit above the support element 7 in the central region of the stationary mold mounting plate 3.

The selected fixing of the stationary mold mounting plate 3 to the machine frame 1 by way of the support element 7 does not involve a change in the position of the stationary mold mounting plate 3 in space under the influence of the closing force. That provides the desired parallelism of mold halves (not shown) arranged on the mold mounting plates 3, 5, even under the influence of the closing force.

FIG. 2 shows a plan view in relation to FIG. 1 in the region of the support element 7. It is possible to see that the further flexural beam 73 is fixed by way of extensions 73′ to the stationary mold mounting plate 3 to provide sufficient space for the flexing of the further flexural beam 73. In other words—if the extensions 73′ are considered as part of the further flexural beam 73—the further flexural beam 73 has a material weakening delimited by the extensions 73′. The central thickening 71′ of the one flexural beam 71 is not absolutely necessary (see for example FIG. 5 where no such thickening 71′ is provided). The extensions 73′ could also be formed as a part of the stationary mold mounting plate 3.

It is preferably provided that at least one additional flexural beam (74) and at least one additional compression bar (72′) are arranged between the further flexural beam (73), the compression bar (72) and the one flexural beam (71).

FIG. 3 shows an alternative to FIG. 2, wherein an adjusting screw 75 is provided for adjustment of the parallelism of the mold mounting plates 3, 5 and therewith the mold halves arranged thereat. By way of the adjusting screw 75 the compression bar 72 can be displaced relative to the one flexural beam 71. Apart from that adjustment option, the flexural beam 71 is fixedly connected to the compression bar 72. FIG. 4 shows a corresponding view of that detail.

FIG. 5 shows an alternative embodiment of the support element 7 (serial arrangement), here comprising three compression bars 72, 72′ and four flexural beams 71, 73, 74 which are arranged serially viewed in the direction of the longitudinal axis L of the machine. The two additional flexural beams 74 here are each of a two-part structure and have a central material weakening. In other words the parts of the additional flexural beams 74 arranged at the right in the Figure have extensions which space them from the parts of the additional flexural beams 74 arranged at the left in the Figure.

An adjusting screw 75 can also be provided in this embodiment.

FIG. 6 shows the support elements 7 detached from the other structures in the deformed condition, that is to say under the influence of the closing force. Only the one half of the support element 7 is shown, the other half is afforded by mirroring at the longitudinal axis L of the machine.

FIG. 7 shows the closing unit in the region of the stationary mold mounting plate 3 in the deformed condition, that is to say under the influence of the closing force. It will be seen that the stationary mold mounting plate 3 remains oriented vertically even in the deformed condition of the leg 2 of the machine frame 1 or of the support element 7. 

1. A closing unit for an injection molding machine comprising a substantially C-shaped machine frame, to the one leg of which is mounted a stationary mold mounting plate and to the other leg of which is mounted a closing mechanism for driving a moveable mold mounting plate in a longitudinal direction of the machine frame, wherein the free ends of the legs of the machine frame are deformed under the influence of the closing force occurring during the closing operation, and wherein the stationary mold mounting plate is supported at or near its lower edge by way of a support element on the machine frame against the closing force and is fixedly connected above the lower edge to the one leg, wherein the support element has a flexural beam extending transversely relative to the longitudinal axis of the machine and a compression bar extending in the direction of the longitudinal axis of the machine, wherein the flexural beam is connected free from backlash to the machine frame, preferably being screwed thereto.
 2. A closing unit as set forth in claim 1, wherein the support element has at least one further flexural beam extending transversely relative to the longitudinal axis of the machine and the compression bar extends between the one flexural beam and the further flexural beam and is connected to both flexural beams.
 3. A closing unit as set forth in claim 1, wherein the support element is connected in the central region of the lower edge to the stationary mold mounting plate.
 4. A closing unit as set forth in claim 2, wherein the further flexural beam or the stationary mold mounting plate has extensions, by way of which the further flexural beam is connected to the stationary mold mounting plate, wherein the extensions are so dimensioned that the stationary mold mounting plate bears against the further flexural beam under a nominal closing force.
 5. A closing unit as set forth in claim 2, wherein at least one additional flexural beam and at least one additional compression bar are arranged between the further flexural beam, the compression bar and the one flexural beam.
 6. A closing unit as set forth in claim 1, wherein the compression bar and optionally the at least one additional compression bar is connected to one of the flexural beams for adjustment of the inclination of the stationary mold mounting plate relative to the moveable mold mounting plate by way of an adjusting screw.
 7. A closing unit according to claim 1, wherein the support element is fixedly connected to the one leg at such a height above the lower edge of the stationary mold mounting plate that approximately a third of the closing force is transmitted into the machine frame by way of the support element.
 8. An injection molding machine comprising a closing unit as set forth in claim
 1. 